This proposal defines a mentored career development plan for a K01 candidate with a long-standing interest in infectious disease research and specialty training in veterinary clinical pathology. The goal of the program is to provide a structured program that will facilitate her development into a veterinary clinician-scientist with an independently funded research program. The candidate's professional development will be guided by her Mentor and Co-Mentor, and by additional scientists who will serve on her mentoring committee. The overall focus of the research project is on formation of extracellular traps by neutrophils (NETs), and their relationship to the pathogenesis of Salmonellosis. NET formation is a rapidly expanding field of investigation, for which there is increasing evidence of relevance to both host defense and immunopathology. NET formation involves extracellular release of chromatin and associated proteins, such as elastase and myeloperoxidase (MPO), which are released from primary granules. These NETs physically trap bacterial cells, making the latter susceptible to inhibition and killing by nearby antimicrobial proteins. There is a brief report that S. typhimuriu induces NET formation by human neutrophils; however, the mechanisms involved in this response are not yet fully understood. Previous research by the candidate and colleagues during her PhD study established that S. typhimurium pathogenicity island-1 (SPI-1) secreted effector proteins contribute to neutrophil migration, fluid accumulation and tissue damage in bovine ligated ileal loop model. These responses may be due in part to chemokine release that attracts and activates neutrophils. Once activated, neutrophils both attempt to eliminate bacterial cells and release mediators that result in local inflammation. The focus of this project is to investigate the role of NET formation in the neutrophil response to Salmonellosis. The central hypothesis is that the S. typhimurium SPI-1 secreted proteins, and elastase and myeloperoxidase (MPO) in the neutrophil granules, participate in NET formation by neutrophils. There are 3 specific aims:1) Define the contribution of S. typhimurium SPI-1 secreted proteins (SipA, SopA, B, D and E2) on activation of NET formation by bovine neutrophils; 2) Determine the contributions of elastase and MPO to NET formation by bovine neutrophils and trapping and killing of S. typhimurium cells by bovine neutrophils; and 3) Use a zebrafish model to interrogate the role of S. typhimurium SPI-1 secreted proteins, and host elastase and MPO in NET formation in vivo. Studying the interaction of S. typhimurium with neutrophils will improve our understanding of the pathogenesis of S. typhimurium-induced enteritis and diarrhea, a significant problem in people and domestic animals. Upon completion of this project, the candidate will have acquired research experience that builds on the candidate's prior training and interests in infectious disease and clinical pathology. This trainin will allow the candidate to be capable of developing an active externally funded research program and to become an independent experimental pathologist.